The introduction and increasing use of several man-made and synthetic fibers have raised concern over their possible health effects in view of their similarity to asbestos, a known carcinogen. Animal studies have clearly indicated the carcinogenic effects of asbestos fibers, Furthermore, the effects of asbestos on cultured cells include cytotoxicity and the induction of chromosome aberrations and cell transformation. We have recently documented the induction of DNA strand damage by asbestos using nick translation. We propose to use the induction of DNA for evaluating fiber genotoxicity and carcinogenicity. Two techniques, nick translation and the single cell gel (SCG) assay, will be used to measure DNA damage induced by asbestos fibers in cultured rat mesothelial cells. The more sensitive technique will then be utilized to quantitate the damage induced by a number of asbestiform, man-made and synthetic fibers. The induced damage will be correlated with animal carcinogenicity data available for the same fibers. Our goal is to determine the applicability of DNA damage assays to anticipate carcinogenicity of natural and artificial fibers.